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High Chlorine Demand

To All
I am a BioGuard Dealer
We use Alex with the medical strip reader AND individual titration as well.
Alex will read TC & FC to 10ppm
as for a chlorine demand in this salt pool a few things to note:

1. Pool Water Temperature: CG's dont work in temps below 55.
2. STOP USING LIQUID CHLORINE - you are not a commercial pool, Commercial pools MUST drain every year because of high TDS levels. Liquid Chlorine is unstable, 12% at the factory, hopefully its a fresh 9% by the
time you put it in your pool - therefore, 91% dissolved solids!
3. Clean the cell.
4. Try treating the demand with both Cal Hypo & Potassium Mono.
5. Or just leave it alone if the pool is crystal clear - set your cell to 80% and let it run 24/7, but clean it first

just a note:
Perhaps I am biased, but I have been in this industry since 1986 from building to chemistry. Many right answers, until you visit CDC and see all the accidents caused by "STRONGER" pool chemicals.

sorry to ramble, just feel the need to educate!!
Good Luck
TimComments promoting a specific brand removed. Promoting your products is not allowed. JasonLion

Re: High Chlorine Demand

As I said in response to your other post about not using liquid chlorine because these are residential pools - frankly that's ridiculous.

Once it's in your pool, chlorine is chlorine is chlorine.

TDS is irrelevant and I've had no problems WHATSOEVER using 6% or 12% ...

MPS is more suited for Spas or indoor pools and it's WAY too expensive to recommend for everyday use in a backyard pool

We recommend using liquid chlorine to boost FC levels - turning up the output or using "superchlorinate" shortens the life of the cell- and quite frankly the cell can't generate chlorine quick enough to do what you suggest, and the FC can be easily consumed by growing algae and unable to keep up.

Re: High Chlorine Demand

Originally Posted by polaris mechanic

1. Pool Water Temperature: CG's dont work in temps below 55.

This varies. Some, like AutoPilot models, will work at quite low temperatures, though not as efficiently as they do at higher temperatures. Others cut off at various temperatures depending on brand, 50, 55, or 60.

Re: High Chlorine Demand

Tim -- Your statement about 91% disolved solids is completely incorrect unless of course, you're considering water as a disolved solid because it has a frozen state that it's not in any longer. How do you get losing 3% strength equals 91% disolved solids. Have you ever worked in a hypo plant?

Re: High Chlorine Demand

Tim,

The Alex system is one of the worst programs available for giving advice to customers in terms of solving their problems quickly and inexpensively. Just one such example of the ridiculous advice given is described in this thread where a combination of the program's lack of understanding of the combination of adjustments from Balance Pak 100 (which is the same as baking soda and raises TA) and 200 (which is the same as Soda Ash which raises pH and TA) along with the recommended addition of Smart Shock oxidizer (which is Dichlor with some copper in it) resulted in a cloudy green pool. There are many posts on this forum about the Alex system such as this one, but the bottom line is that it reads test strips and these are not as accurate as liquid based colorimeters PLUS the computerized diagnostic program is designed to sell chemicals, not solve problems intelligently.

Chlorinating liquid does degrade over time, but it isn't "unstable" in the sense that such degradation will occur in days. The chart at the bottom of this page shows that even 15% chlorinating liquid stored at 80ÂºF will have a half-life of 100 days (over 3 months). In practice, most chlorinating liquid is 10% or 12.5% which lasts longer and at decent pool stores the turnover of such chlorinating liquid is fast enough that it is nearly full-strength by the time it gets used. I have personal experience with this since I buy 12.5% chlorinating liquid from my local pool store and have measured its strength as well as seen the expected FC rise in my pool when used. I also keep 4 gallons over about a month to use and notice virtually no decline in strength (our average day/night temps are around 70ÂºF with a few peak days that might get to 90ÂºF).

Clorox Regular Bleach as well as most off-brand Ultra bleaches are 6% and last about 4 times longer than 12.5% chlorinating liquid. Degradation is rarely an issue here unless the turnover at the grocery store is exceptionally low.

Chlorinating liquid is mostly water, NOT 91% dissolved solids. Yes it is true that chlorinating liquid, bleach, and lithium hypochlorite all have salt in them, but ALL sources of chlorine result in salt since chlorine turns into chloride (salt) when it gets used up. For every 10 ppm FC that is consumed, this results in 8 ppm salt. With chlorinating liquid, bleach and lithium hypochlorite, there is an additional 8 ppm salt upon addition for a total of around 16 ppm salt after the chlorine is used up. Salt is relatively innocuous and it takes quite a while to build up the TDS level. Residential pools are typically low bather load so have increasing salt levels at a much slower rate than commercial pools. Also, winter (and summer, depending on area) rain overflow along with backwashing filters dilutes the water often keeping the salt level in check.

As for your suggestion of using Cal-Hypo, for every 10 ppm FC this increases the CH by at least 7 ppm. So unless your CH is already on the low-side, there is no reason to use Cal-Hypo. As for MPS, that's very expensive -- about 3-5 times more expensive for the same FC equivalent in terms of oxidation as compared to chlorine. If a pool has ammonia in it upon opening, for example, MPS won't clear the pool that much faster than chlorine. If it's algae growth, MPS will be worse than chlorine at clearing the pool since chlorine kills algae much faster than MPS does.

There are over 20,000 members of The Pool Forum and over 10,000 members here at TFP who manage their pools through a proper understanding of their water chemistry using good test kits (including FAS-DPD for chlorine tests) and through sound chemical principles rather than incorrect or incomplete information that is generally promoted in the pool/spa industry. There are also quite a few of us on this forum who look at actual chemistry, do experiments, correlate data, and question industry information to get to the real truth. I suggest you get a deeper and more accurate education by reading this thread that corrects or enhances much of the education in the current CPO course/manual or you can start with the Pool School for a less technical introduction to what we have learned.

Re: High Chlorine Demand

All forms of chlorine contain salt. Bleach/liquid chlorine does have more salt in it than other kinds of chlorine. But even so, it doesn't have enough salt to cause any problems. Even after many many years of using bleach/liquid chlorine, the salt level still won't have gotten as high as is routinely used with a SWG.

Originally Posted by polaris mechanic

Commercial pools MUST drain every year because of high TDS levels.

This isn't true most places, though it is true in a few places. The laws haven't kept up with the technology very well. There are still a few places where the law was written back when TDS was used as a proxy for the CYA level.

Long ago they didn't have a CYA test, didn't know that they needed a CYA test. Someone noticed that pools with high TDS tended to have problems. The problems were being caused by high CYA levels, but they didn't know that. When a pool is cared for the way they cared for pools back then, the CYA level would just go up and up and the TDS level would also go up and up, so TDS could be used as a rough proxy for the CYA level.

These days, pools are managed in different ways and CYA tests are easy to get. Some systems for managing pools still have the TDS and CYA level going up together, but other systems for managing pools, such as the one we teach here, don't. TDS no longer reliably indicates what the CYA level is. Instead, you can measure the CYA level directly and just ignore TDS.

Meanwhile there are still a few places where the law is written based on the old understanding, though there are fewer and fewer of them each year. In those places commercial pools need to keep the TDS level low because that is the law, even though it doesn't make any sense anymore.

Re: High Chlorine Demand

Also, in high bather-load pools, as with some commercial and many public pools, the TDS can be used as a rough proxy for the amount of unoxidized organics in the water -- sort of an "age" of the water. Such a proxy falls apart in a low-bather load outdoor pool such as most residential pools because the primary usage of chlorine is in breakdown from the UV in sunlight and that results in salt without unoxidized organics.

Re: High Chlorine Demand

Re: High Chlorine Demand

Again, it depends on what individual constituents make up that TDS reading. Most of a TDS reading consists of NaCl, some CaCl2, and various other inorganic, inert compounds. If some of that TDS consists of organics, reducing agents such as ascorbic acid, ammonia, etc., then those compounds will consume chlorine and contribute to the demand. The point that the above posters are making is that TDS lumps all of these things together, meaning that the bulk number tells you nothing.

Say, for example, you have 6000 ppm TDS in your pool. 5975 ppm of that consists of salt, calcium, etc., and do not contribute anything to the chlorine demand. The last 25 ppm is ammonia, consuming chlorine like crazy. The 6000 ppm TDS level does not tell you that's what's happening. It can't tell the difference between that situation and 6000 ppm NaCl, which would do nothing to chlorine demand.

Re: High Chlorine Demand

It all depends on what specific chemicals are producing the TDS reading. TDS in and of it's self doesn't tell you what you need to know. If you raise the TDS with salt, you can raise the TDS as high as you want and there won't be any significant effect on the chlorine demand (at least up to TDS levels in the 40,000 range). On the other hand, if you raise the TDS level with CYA or trichlor there will be problems and many people would describe those problems as an increased chlorine demand (though actually something more complicated is going on).

Another way to look at this has to do with what chemicals you use to maintain you pool. If you consistently use trichlor and/or dichlor then there will be a correlation between TDS and increases in chlorine demand. However, if you consistently use a SWG, or bleach, or liquid chlorine, or cal-hypo there won't be a correlation between TDS and increases in chlorine demand.

Ultimately, TDS isn't the number you want to be looking at. The three largest contributors to the TDS level are usually Salt, CYA, and CH. In terms of chlorine demand, you want to be looking at the CYA level. If you have a SWG you want to be looking at the salt level. If you have a plaster pool, or live in an area with high evaporation rates, you want to be looking at the CH level.

Given specific pool chemicals that are routinely used in a particular pattern, you can use TDS as a proxy for any of these three levels. But in each case, it is more reliable to just measure the appropriate level directly.

There are a few second order effect of high TDS levels. The increased ion levels in the water affect chemical reaction rates just slightly. But for plausible TDS levels (say 0 to 4,000) the changes are very small and can be ignored. TDS also has a small effect on the calcium saturation index, but again the effect is small and can be ignored. Indeed, the traditional way of calculating the calcium saturation index ignores TDS completely.

Re: High Chlorine Demand

Originally Posted by Beez

If you look up just 4 posts previous, chem geek answered your question very succinctly...

I didn't explicitly write about TDS and chlorine demand, though I did discuss about how chlorine addition and consumption increases salt levels so contributes to TDS. I said salt is relatively innocuous, but didn't explicitly say that it does not contribute to chlorine demand. Anyway, Melt in the Sun and Jason both answered that specific question. The bottom line is that TDS is too broad a measurement that by itself doesn't relate to anything useful; it is what TDS is composed of that is relevant and there are separate tests for measuring those components (i.e. FC, CC, pH, TA, CH, CYA).

The most common scenario in pools that use stabilized chlorine is that the CYA level builds up and results in nascent algae growth (because the FC/CYA ratio becomes too low) that then appears as increased chlorine demand long before the water actually turns dull or cloudy. Eventually, if the FC level isn't raised in proportion to the FC, the algae growth outpaces the chlorine algae-killing rate and the water turns dull and then cloudy and then green (or other combinations or steps, depending on the type of algae). In SWG pools, something similar happens though the CYA isn't climbing -- the recommended FC from SWG manufacturers is too low since 1-3 ppm with 80 ppm CYA isn't a high enough FC/CYA ratio to prevent algae growth under all reasonable conditions.

Re: High Chlorine Demand

Tim, I just wanted to say welcome to TFP

Hopefully you have read through Pool School by now and tried to understand the BBB method and the forum's purpose? Coming on this forum and telling folks to stop using liquid chlorine, will yeild you a lot of interesting discussion

The forum's purpose is to teach us to understand what is going on with our water.chemistry With all due respect to your experience, I have spent $100's on the products that you sell, and by all means they probably work for most of your customers...but it costs them in the long run b/c they are clueless about water chemistry. Read through pool school if you really want to understand how trouble free pool maintaince can be. It cost me about $300 to maintain my pool last season, and that included a $65 test kit, a $135 SWG (cheap I know) and 300-400 lbs of salt (plain old water softner solar salt @$4 per 40 bag)...this year should be half that cost. Bottom line...I did not shock once...all season. When I relied on a system from a pool store that told me what what to add...blah blah blah...I just kept writing checks and never having clear water.

I respect your experience, and our method may be a little unconventional, but you won't find another pool forum that is as successful as TFP...bottom line, most of us came here after being pool stored for many years, so you're probably fighting a losing battle, but if you stick around, you'll learn a ton of stuff that you thought you already knew.

Welcome and we appreciate your input thus far...especially the info on the Polaris models you are familiar with. Thank you

PS...I would think the granular chlorine has just as many undisolved solids and if you use enough of it you'll be draining your pool anyway due to high CH or CYA....just some food for thought.

Re: High Chlorine Demand

If you look up just 4 posts previous, chem geek answered your question very succinctly...

I didn't explicitly write about TDS and chlorine demand...

Sorry Richard, didn't mean to put words in your mouth! FWIW, this is the statement I was referring to:

Originally Posted by chem geek

Also, in high bather-load pools, as with some commercial and many public pools, the TDS can be used as a rough proxy for the amount of unoxidized organics in the water -- sort of an "age" of the water. Such a proxy falls apart in a low-bather load outdoor pool such as most residential pools because the primary usage of chlorine is in breakdown from the UV in sunlight and that results in salt without unoxidized organics.

To my mind, this answers Tim's question very well even if you have to read between the lines a little...in other words, in certain situations such as "in high bather-load pools, as with some commercial and many public pools..." TDS can contribute to an increased chlorine demand specifically because in that situation, "the TDS can be used as a rough proxy for the amount of unoxidized organics in the water..." However, TDS doesn't apply to the pools that we are concerned with because: "Such a proxy falls apart in a low-bather load outdoor pool such as most residential pools because the primary usage of chlorine is in breakdown from the UV in sunlight and that results in salt without unoxidized organics."

I realize this is a simplified answer, but I don't think it is always necessary to give a detailed chemical analysis to answer a question succinctly. Honestly, I'm not sure the OP cares too much about the details anyway. The short sweet answer is: What you have been taught about TDS applies to commercial or public pools, but not so much with private residential pools.

Unless, of course, I'm completely wrong, then: Nevermind...

Sorry for the long convoluted post, just wanted to clarify my comment. We are in the deep end aren't we?